While the degree of rivalry in a market is often concealed and therefore difficult to observe directly, various measures of market share variation have been used in the literature as an indicator of behavior. Using a similar measure, the primary task of the study was to estimate the degree to which rivalry (both price and non-price) had actually increased during the first two years of deregulation. The paper also provides an analytical framework which may be used to assess the impact of regulatory reform on rivalry in other industries.